The present invention relates to machine tools in general, especially to grinding machines, and more particularly to improvements in machine tools for the treatment of special types of workpieces. Still more particularly, the invention relates to improvements in machine tools for removal of material from consecutive workpieces of the type having pairs of surfaces to be treated and wherein such surfaces are disposed opposite each other. Typical examples of such workpieces are twin-bladed knives of the type used in hedge cutting or trimming apparatus. The cutting edges of such knives are disposed diametrically opposite each other, i.e., it is necessary to turn the knife through 180 degrees if the grinding or another treatment of one cutting edge by a tool is to be followed by the grinding or another treatment of the other cutting edge by the same tool.
As a rule, twin-bladed knives for use in hedge trimming or like apparatus are assembled into a package or stack and the stack is confined in a receptacle, known as cassette, which affords convenient access to both cutting edges of each knife of the confined stack. Consequently, when the cassette is inserted into a grinding machine or another machine tool (e.g., a lapping machine), the grinding wheel or another suitable material removing tool can treat one cutting edge of the entire stack of knives before the cassette is inverted so as to place the other cutting edge of each knife in the stack into the range of the material removing tool. As a rule, the inverting operation is carried out by hand and must be preceded by detachment of the cassette from the work holder and followed by reattachment of the inverted cassette to the work holder. The treatment of the other cutting edge of each of the knives in the cassette is followed by detachment of the cassette from the work holder and manual removal of the cassette from the machine tool so as to provide room for manual insertion of the next cassette. Such mode of manipulating cassettes with stacked workpieces, each of which has two surfaces that require treatment by a material removing tool, is a tedious, time-consuming and ineconomical procedure which does not allow for full-capacity operation of a modern machine tool, such as a grinding machine.